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BTW, polyester is much more resistant to UV than nylon. That's why it's possible to see tents with polyester flies that won't advertize UV resistant coatings. This doesn't mean they are inferior. The downside is that the polyester flies usually discolor faster even though the fabric is still strong.
– Gabriel C.Nov 9 '18 at 18:29

From my experience, a tent standing under the hot desert sun for a couple of months won't last more than 2-3 years. Of course, there are other factors like a wind or sandstorms, but the fact is that tent fabric becomes brittle and tears apart.
– UsurerNov 12 '18 at 11:16

3 Answers
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UV damage occurs when long term exposure to the sun damages the fabric and thread of your tent or rain fly. The fabric will become thin and brittle. If you tent or rain fly seems to rip for no reason or with very light pressure, this could be the reason. The outside of the fabric will often appear to be a much lighter color than the inside.

Ultraviolet damage to tent fabric is caused by excessive exposure to sunlight. While our fabrics are UV resistant, any synthetic fabric is susceptible to ultraviolet degradation. UV damage will cause nylon and polyester to become brittle and tear easily.

A tent's UV resistance isn't for you, it's for the tent. High-energy UV rays will break down many synthetic and natural textiles over time. UV resistant fabrics are not as susceptible to this breakdown, and will last longer with repeated exposure to sunlight.

UV resistant fabrics are great if you're looking for long-lasting gear that will be used in exposed, sunny areas, like above the tree line on a mountain. If you're doing occasional camping in a shaded forest, it may not be as much of a selling point.

It is for two reasons. By far, the primary concern is that UV rays will make the textiles deteriorate over time. UV resistant textiles will last a lot longer, and deteriorate less from only sunlight.

It is also a minor concern for the people inside, but only if they will be spending considerable amounts of time in the tent in direct sunlight. Similar to how its possible to get a sunburn through thin clothing if you are out long enough, a small amount of UV rays will pass through a non-UV resistant tent and reach the people inside. Usually this isn't a concern, but if you spend all day every day in the tent without sunscreen, then you would have the potential to get tanned or burned

I am skeptical that UV resistance on the tent has any correlation to protection of contents (like a human). Are you presuming such a correlation or do you know there is?
– wallykNov 12 '18 at 0:48

@wallyk There is a correlation. Again, the main concern is the ability of the material to not breakdown quickly. However, some people who spend a considerable amount of time in a tent (the homeless, travelers, or workers of some jobs where you live in your own tent during the summer season) should consider the UV resistance of the material for their own health, to reduce the risk of melanoma / skin cancer / premature aging. UVF is the unit of measurement used for clothing for this purpose. link
– Alex CobaltNov 13 '18 at 20:27